Hydrologic Applications

Hydrologic Question

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Learn about hydrologic applications of isotopes. Isotope studies can be useful in hydrology in answering the following questions.

What is the source of the water?
 

What is the age of the water?
 

What is the source of solutes (including contaminants) in water?
 

Isotope or Chemical Tracer

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Geochemical and isotopic tracers and their application in water resources problems.

GEOCHEMICAL ISOTOPIC TOOL (1)INERT TRACERS ROLE AS TRACER
Cl Master variable: inert tracer in nearly all geochemical processes, use in recharge estimation and to provide record of recharge history
Br/Cl Use to determine geochemical source of Cl
36Cl Half life 3.01x105 yr.Thermonuclear production - use as tracer of Cl cycling in shallow groundwater and recharge estimation. Potential value for dating over long timespans and also for study of long term recharge processes. However, in situ production must be known
37Cl/35Cl Fractionation in some parts of the hydrological cycle, mainly in saline/hypersaline environments may allow fingerprinting
3H Recognition of modern sources of salinity (half life 12.3)
δ18O,δ2H Essential indicators with Cl of evaporative enrichment and to quantify evaporation rates, in shallow groundwater environments. Diagnostic indicators of marine and palaeomarine waters
Noble gases and noble gas isotope ratios    
δ34S Indicator together with δ18O in the dissolved sulphate to obtain information on salinisation causes, eg dissolution of evaporates or salt water intrusions
CFCs, SF36 Essential indicators with Cl of evaporative enrichment and to quantify evaporation rates, in shallow groundwater environments. Diagnostic indicators of marine and palaeomarine waters
(2) REACTIVE TRACERS ROLE AS TRACER
Major ions, Major ion ratios Ca, Mg, Na,K; HCO3, SO4, (Cl) the major ions in groundwater are derived from water rock interaction and their concentrations and ratios (to each other and to Cl) may be diagnostic of rock type and residence time
Mg/Ca Diagnostic ratio for (modern)sea water
Na/Cl Ratio increase diagnostic of cation exchange reactions
Trace elements and trace/major element ratios Sr, F, Li and others diagnostic of lithology, residence times etc
Nutrient elements (NO 3 ,K., PO 4 ) Nitrate accumulations may accompany Cl in aerobic arid environments. Nutrient elements characteristic of irrigation returns
87Sr/86Sr Additional indicator of source of groundwater source rock with more radiogenic ratios (higher 87Sr derived mainly from igneous rocks
δ11B Additional indicator of salinity source
14C, δ13C Radiocarbon activity expressed as percent modern carbon is proportional to groundwater age. Half life 5730. Understanding of carbon geochemistry is essential to interpretation
TOC Indicator of organic contamination. Natural baseline levels rarely exceed 2 mg/l
δ13C Indicator of organic degradation and calcite dissolution. Also biogenic pollution
δ15N Indicator of urban pollution and source of nitrification in urban areas
Organics Indicator species (eg fatty acids) to characterise marine waters of different age. Pesticides etc diagnostic of irrigation sources of salinity
Dissolved gases